parisc: Don't enforce DMA completion order in cache flushes

The only place we need to ensure all outstanding cache coherence
operations are complete is in invalidate_kernel_vmap_range. All
parisc drivers synchronize DMA operations internally and do not
call invalidate_kernel_vmap_range. We only need this for non-coherent
I/O operations.

Signed-off-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>